The invention relates to a method for installing a scrolled resilient sheet alongside the inner surface of a fluid conduit.
It is known from U.S. Pat. Nos. 4,501,327 and 5,040,283 to scroll a sheet around a carrier tool and then move the carrier tool carrying the scrolled sheet through the conduit towards a location where the resilient sheet is to be installed, whereupon the sheet is released from the carrier tool and allowed to expand towards the inner surface of the conduit.
U.S. Pat. No. 5,040,283 employs a sheet made of a memory metal which expands as a result of a temperature increase. A drawback of this method is that memory metals are expensive and are not readily available in large sheets.
U.S. Pat. No. 4,501,327 discloses the use of spring steel or aluminum as a resilient material, which materials have an elastic strain which is 0.55% or less (0.2% for aluminum) and that a suitable thickness for the sheet material is approximately {fraction (3/64)} inch (=1.2 mm).
In this known method the resilient material is pressed against the wall of the conduit when the carrier tool is pulled back through the expanded sheet.
Drawbacks of this known method are that a relatively thin sheet material is used which can be easily damaged and which has a resiliency which is only sufficient to unscroll the sheet but which does not induce the sheet to press itself into place alongside the inner wall of the conduit so that a final pressing step is still required.
It is believed that the low wall thickness of the known aluminum or spring steel sheets and the relatively low expansion force are associated with the low elastic strain capacity of the materials used.
It is an object of the present invention to eliminate these drawbacks and to provide a method for installing a scrolled resilient sheet alongside the inner surface of a fluid conduit which allows the use of a relatively thick and robust sheet which is not easily damaged after installation and which does not require the-step of pressing the sheet alongside the wall of the conduit by means of an expansion tool.
Toward providing these and other advantages the method according to the present invention employs a resilient sheet which has an average wall thickness of at least 2 mm and an elastic or pseudoelastic recoverable strain of at least 0.6% so as to induce the scrolled sheet to expand with an expansion force which is sufficiently high to allow the sheet to press itself into place alongside the inner surface of the conduit during installation and to remain in place after installation.
When used in this specification the term elastic strain refers to the yield stress-Young""s modulus ratio for materials which have a yield point, like many carbon steels have, or the proof stress-Young""s modulus ratio for materials which do not have a yield point. If the elastic strain is expressed as a percentage then said ratio""s are to be multiplied by a factor of 100.
Preferably the resilient sheet has an average wall thickness of at least 3 mm and is made of a titanium alloy having an elastic modulus not more than 115.000 MPa and a proof stress of at least 825 MPa, so that the elastic strain is more than 0.75%.
It is also preferred that the resilient sheet material has an average wall thickness of at least 4 mm and is made of a Ti-6Al-4V alloy.
The sheet may be a rectangular sheet without perforations which is used to provide a seal or a patch of an area where the wall of the conduit has been ruptured, damaged or eroded. Alternatively the fluid conduit is formed by an inflow region of a hydrocarbon production well and the sheet is perforated at regular intervals and is installed alongside the inner surface of the wellbore to serve as a wellscreen.
If the sheet is to be scrolled to a very small diameter, for example if it is to be moved through constrictions in the conduit, then it can be beneficial to use a pseudoelastic alloy as sheet material. Suitable pseudoelastic alloys are Ti-16V-3Al-6Zr and TiNi.